CA2091847A1 - Preparing and coating a glass substrate - Google Patents

Abstract

PREPARING AND COATING A GLASS SUBSTRATE

Abstract of the Disclosure Glass is primed with a clear coat which is a mixture of an organosilane and an organotitanate. Subsequently the primed glass is coated with a coating composition comprising a fluorocarbon, an organosilane and/or an organotitanate, an inorganic pigment and a thermoplastic polyacrylate resin that has no functional groups reactive with the organosilane or organotitanate, the coating composition being carried in an organic solvent.

Description

PATENT

PREPARING_AND COATING A GLASS SUBSTRATE

The present inven~ion is directed to priminq a glass substrate for coating and subsequently coating the glass substrate with a polyvinylidene fluoride/acrylic resin coating containing inorganic pigments.
BACXGROUND OF THE INVENTl N

The present invention is direc~ed to an improved method of coating a glass substrate with pigmented coatings in which the resin system is a mixture of a fluorocarbon and a thermoplastic polyacrylic resin.
Fluorocarbon-based coating compositions have been recognized to Aave excellent w~-athering propertie~, including gloss retention, water resistan~e and color retention. The present invention is directed to coating glass with a fluorocarbon-based coating composition in a manner that provides excellent adherence o~ the coating to the glass. Glass so coated may have widespread application in curtain walls where they may provide economic ~dvantages relative to aluminum skins tha~ are curren~ly used.
A lo~g recognized problem of glass coated wi~h a fluorocarbon-based coating is obtaining adequate adherence of the coating to the glass.

P~T~I~T

~.S. Patent No. 4,879,345 to Connelly et al., issued November 7, 1989, teaches a coating composition of a fluorocarbon, an organosilane, an acrylic resin having functional groups reactiv~ with the organosilane and (optionally) pigments and fillers. This coating is applied directly to the glass surface, and it is theorized that the organosilane forms bonds between the glass and the functional acrylic resin.
V.S. Patent No. 4,510,282 to Goll, issued April 9, 1985, teaches a composition which is an aqueous dispersion of polyvinylidene fluoride (PVDF), acrylic co-polymer and pigment.
Examples are given in which the composition also contains an organosilane. Thi~ reference t~aches ~at the woxk material may be pre-treated with gamma-methacryloxypropyltrimethoXy-silane and then pre-impregnated with up ~o ~hree coa~s of a PVDF latex prior to adding the coa~ing composition. While the pre-treatment of the work ma~erial with organosilane may promote bonding to the PVDF later, the subsequent pre-impregnation with PVDF later would prevent bonding directly between the organosilane on the work material and components of the coating material. Although water-based system5 are desirable from an emissions and environmen~al point of view, organosilanes are unstable in the presence of water, converting to silanols and then to siloxanes. Thus a water-based coating composition would la k long-term stability, changing in silane co~position over time.
- The present invention is directed to an improved method of coating glass with a fluorocarbon-based coating composition.

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PATEN~

SUMMARY OF THE_INVENTION

In accordance wi~h the presen~ inv~ntion, a properly cleaned glass substrate is ~irst primed with a clear, dilute solution of a mixture of an organosilane and an organotitanate. A coating composi~ion is applied which comprises a fluorocarbon resin, an organosilane and/or an organotitanate~ a thermoplastic polyacrylate resin having no groups reactive with the organosilane and/or an organotitanate, and an inorganic pigment, the components being carried in an organic solvent. Two successive coatings may be applied to a surface of a glass substrate, each having a pigment level and being applied to a sufficient thickness to be fully opaque and thereby give distinctly differen~ appearances to ~he glass~ which is coated on only one side, as vie~ed from opposite sides.
DETAILED DESCRIPTION OF CERT~IN PREFERR D EM~ODIMENTS

Fluorocar~ons useful in forming the coating compositions o~ the present inven~ion include polyvinyl fluorides, polyvinylidene ~luori~es (PVDF), vinyl fluoride copolymer~ and vinylidene ~luoride copolymQrs. The preferred fluorocarbon is po1yvinylidene fluoride. The copolymers preferably include at least ab~ut 75 wt.% and preferably at le~st abou~ 90 wt.% vinyl ~luoride or viny1idene fluoride monomers. Examples of monomers which may be copoly~erized with vinyl fluoride or vinylidene fluoride are e~hylene, propylene~ isobutylene, styrene, difluorochloroethylene, tetrafluoroethylene trifluoropropylene, h~xafluoropropylene, vinyl formate, :: - 3 -PATENT
2090~30-24 vinyl acetate, vinyl propionate, viny~ ~utyrate, acrylic acid and its salts, methyl methacrylate t allyl methacrylate, acry}onitrile, methacrylonitrile, N-butoxymethyl acrylamide, allyl acetate and isopropenyl acetate.
The fluorocar~on comprises between abou~ 50 and about ~0 wt. percent of the resins of the coating, the thermoplastic polyacrylate resin compri~e~ between a~out lo and about 50 wt. percent of the resi~s. Herein, unless otherwise ~tated, non-rPsin components will b~ expressed as parts per hundred (phr) resin based upon the total amount oP
resin, including the fluorocarbon and the polyacrylate.
A mixture of an organosilane and an organotitanate is used as a primer to treat the glass ~urface. An organosilane or organotitanate is ~lso incorporated in the pigmented coating or coatings~
Organosilanes, such as ~hose described in above-referenced U.S. Patent No. 4,879,345, are useful in the pr~
invention both for applica~ion as a clear pri~er and as a component of the pigmented coating or coatings. Some preferred organosilanes for use in ~h~ method of the present invention are gamma~methacryloxy propyltrimethoxysilane, gamma-a~inopropyltriethoxysilane, gamma- -glycidoxypropyltrimethoxysilane, gamma-~ercaptopropyltrimethoxysilane, beta-3,4-epoxycyclohexylethyltrimethoxysilane, gamma-aminopropyltrime~hsxysilane, aminoethyla~inopropyltrimethoxysilane, gamma~
methacryloXypropyltrimethoxysilane, vinylbenzyl (trimethoxysilyl) propyl mono hydrochloride, 1,2-bis (trim~hoxy~ilyl) ethane, phenylaminopropyl~ri~ethoxysilane, 3CH-styrylmethyl-2~amino ~tAylamino propyl~rimethoxysilane hydrochloride, vinyltrimethoxysilane, N-C3-acryloxy-2-hydroxypropyl)-3-amino-propyltriethoxy~ilan~, " , . . .
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PAT~NT
2090-30-2~
N 2(vinylben~ylamino)-ethyl-3-aminopropylkrimathoxysilane mono hydroqen chloride, 3-(N-styryl~ethyl-2~
aminoethylamino)-propyl rimethoxysilan~ hydrochloride and triethoxysilyl modifiad polybutadiene.
Suitable organotitana~es include, but are not limited to, tetraisopropyl titanate, tetrabu~yl titanate, and tetra~is (2-ethylhexyl) ~itanate. Also, titanate chelates, such as titanium bis(ethyl-3-oxobutanolato-O1,03)bis(2-propenolato)-, ethanol, 2, 2' 2"-nitrilotris-, titanium(4+)salt, and ti~anate (2-),dihydroxy bis [2-hydroxypropanato (2-)_ol,o2]-, are suitable.
In the pri~er, the organosilane and organoti~anate are mixed together at a weight ratio of be~ween about 5:1 and about 1:5, preferably between about 2:1 and about 1:2.
The organosilane/organoti~anate primer is applied to a glass surface, generally as a dilute, e.g., 2-25 wt.%, solution in an organic solvent ~5) . The organosilane/organotitana~ primer is preferably applied to between about 1.0 and a~out 5.0 ~m. (organosilane plus organotitanate) per m2. In pigmente~ coating compositions in accordance with the present invention, organosilane and/or organotitanate is used at between about 2 and about 12 phr, preferably betw~en about 3 and about 6 phr.
Above-referenced U.S. Patent No. 4,879,345 t~aches that an acrylate adjuvant resin having functional groups reactive with the organosilane is necessary to obtain adequate adhesion. Surprisingly and unexpectedly, it is found that in a coating composition containing an inorganic pigment or filler, it is preferreA that the thermoplastic acrylate resin b~ non-reactive with the organosilane or the organotitanate of the primer or the organosilane or organotitanate o~ the coating composition. U.SO Patent No.
4,879,345 proposes thak by using an organosilane-reactive ~, .

PA~ENT

adjuvant resin, a bond is formed between t.h~ glass and the adjuvant resin. Although applicants are no~ bound by theory, evidence applicants have accumulated indicates that in an inorganic piymen~-con~aining coating composition, a bond is formed ~hrough the organosilanes and organotitanate directly between the glass and the inorganic pigment particles, thereby achieving a s~ronger bond between the glass and the coating.
Preferred polyacrylates are polymers and copolymers formed from esterified acrylates having no additional functional groups, such as esters of acrylic acid and methacrylic acids with mono-functional alcohols. ~owever, in accordance with the lnvention, the polyacrylates may have functional groups, providing they do not co~tain any significant amounts of functional groups reactive with the organosilane selected. On an equivalence basis, the polyacrylate resin should con~ain no more ~han bout 10%
relative to co-reactive groups of the organosilane or organotitanate in the coating composition and preferably no co-reactive groups at all. This allows all bonding to take place b~tween the organo~ilane and organotitanate, both in the primed glass surface a~d in the coating composition, and the inorganic pigment or fill2r.
Th~ inorganic pigment or filler i5 us~d at a level of at least 2 phr, up to about 150 phr. Preferably, the selected pigment or filler is neither acid nor water sensitive. Examplec of inorganic fillers useful in the present invention are silicates; such as mica, aluminum silicat~ and glass par~iculatest inorganic oxides, such as titanium dioxide; strontium chromate; and barium sulfate.
It is believed that the excellent glass-to-coating bonding achieved b~ the method of the present invention is a result of direct chemical bonding be~ween the glass and some ~ ~ 6 ~
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PATENT
209~-30-~4 of the inorganic pigment particles. It i5 believed that the absence of reactive func~ional groups on ~he acrylic resin, prevents khe depletion of organosilane and organotitanate by reaction with the polyacrylate resi~ and t:he organosila~e and organotitanate, which such raaction would result in bonds that are less s~rong ~han the bonds bgtwe~n the glass and the inorganic filler ~hrough the organo~ilane and organotitanate.
The coating composition may contain other components well known in the art, including W -inhibitors, colorants, ceramic fiber, and organic pigments. Although organic pigments may be used in addition to inorganic pigments, organic pigments are found not to significantly promote bonding of the coa~ing to the glass. Indeed, if organic pigments are used in the absence o~ inorganic pigments, there is insufficient bonding o~ ~he coa~ing to the glass.
The types and amounts of pigments and coloran~s and the thickn~ss to which the coating is applied de~ermines the appearance of the final pro~uc~. Typically ~he coa~ing is applied directly ov~r the primed glas~ ~o a thickness of between about S and about 50 micr~ns. The appearance o~ the coating may range from translucent, as is desirable for a lighting fixture, to fully opaque, as is g~nerally desirable in curtain wall panel~.
In o~e a~pect of ~he i~ven~ion~ a glass substr~e will be prim~d, coated with a ~irs~ coa~ing, as described above, th~ first coating containing suf~icient pigment and bein~
applied to a thickness as to ~ fully opaque and then coated with a second coating, as da~cribed above, al~o containing sufficient pigment and being applied to a ~hickness as to be fully opaque. Through the us~ of different pigments and colorants, each side of the glass may have entirely di~ferent appearances. This may be particularly desirable , , :.: , :. : . , ~

PATENT

in curtain wall panels, particularly t~ose used in the interior of a building, where a glass panel coated on one side only, but with two coats, can have entirely different appearances when viewed from opposite side~s.
Be~t results are obtained when the glass i5 thoro-lghly cleaned. One very suitable protocol involve~: 1. rinsing with water, 2. polishing with an abrasive, such as cerium oxide, 3. rinsing with water, 4. cleaning with a deteryent solution, 5. rinsing with deionized w~ter, and 6. drying.
The unpigmented organosilane/organotitanate primer is carried in an organic solvent as is the pigmented coating composition. Suitable organic solvents include, but are not limited to toluene, xylene and mixtures thereof.
Preferably, the primer composition is water-~ree particularly i~ the primer contains organosilane, as water tends to degrade organosilane. Generally, primer compositions in accordancP with the inv~ntion are applied at between about 1 and about 45 percent solids; pigmented coatings are typically applied at be~ween abou~ 10 and about 55 percent solids. The me~hod of applying the coating may determine the percent solids of application. The primer is typically applied by spray coating and then dried prior to application of the coating co~position. The coating composition may be applied by a variety of me~hod~, such a~
spray coating~ roller coating, silkscreen, curtain coating, and electrostatic spray coating, such as that involving turbodisks and turbobells.
After application, the coating is dried, typically at elevated temperatures. After the coating(s) is applied and dried, it is typical to bake the coating to fuse the resinous material and promote bonding of ~he coating to the glass. Baking is typically at between abou~ 200 and about 250C~ If more than one coating is applied, baking :
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PATE~NT
2090-30 ~4 generally follows application and drylng of the two coatings.
Coatings produced in accordance with ~he present invention have proven to be ex~remely stronyly bonded to glass substrates. It has proven difficul~ to scrape coating from a glas~ substrate without scraping away glass itself.
Coatings in accordance with the present inven~ion are highly resistant to water, including boiling water and humid atmosphere.
The coatings may be applied to any glass substrate.
For curtain wall panels, particularly exterior curtain wall panels, tempered glass is preferred for safety reasons.

The invention will now be described in greater detail by way of specific examples.

Examples 1-7 ~all parts by weight unless stated otherwise) Example 1 Tetra ~2-~ethoxyethoxy) silane 2.5 parts Tetrabutyl titanate 2.5 parts Tetrapropyl orthosilicate2.5 parts Naphtha (petroleum light aromatic) 42.5 parts Toluene 25.0 parts Example 2 (pigmented coating composition) parts Thermoplastic acrylic resin*10.31 (60,000)MW(wt.ave) Toluene 12.93 Iron oxide 10.30 _ g _ ~, :: ,.
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-PATENT
2090-30_24 "Kynar 500" (PVDF) Butyl "Cellosolve"2 24-Di-methyl phthalate 8.77 3-ethoxy propionate 8.25 ~3-glycido~xpropyl)trim2thoxysilane 2 o *polymethylmethacrylate (ACRYLOID B-44 , Rohm & Haas) Example 3 (pigmented coating composition) Thermoplastic acrylic resin (60,000) MW (wt.aveJ 10.54 Mica (3-48 micron) "Kynar 500"l 8.31 3-ethoxypropiQnate 24.42 Butyl "Cellosolvel'2 11.19 Di-methyl phthalate Toluene 8.88 Lampblack, iron oxide (3-glycidoxypropyl)trimethoxysilane 1 96 l. Trade Mark 2. TFade Mark,Butyl "Cellosolve" is ethylene glycol monobutyl ether (2-butoxyethanol) 3- Trade Mark .. ..
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PATENT
2090-30~24 Example 4 (pigmented coating composition) Ther~oplastic acrylic resin 11.63 (60,000) MW ~wt.ave) Toluene 12.15 Lampblack 1.90 "Kynar 500"* 27.32 ~utyl "Cellosolve"* 9.70 Di-methyl phthalate 9.13 3-ethoxy propionate 10.49 N-2(vinylbenzylamino)-ethyl-3-aminopropyltrimethoxysilane mono(HCl) 1.96 Example 5 (pigmented coating composition) Ther~oplastic acrylic resin 8.96 ~60,000) MW (wt. ave) Toluene - 12.97 Titanium dioxide 14.97 "Kynar 500"* 21.07 Butyl "Cellosolve"* 8.80 Di-methyl phthalate ~.29 3-ethoxy propionate 9.70 3-methacryloxypropyl-trimethoxysilane 2.00 * Trade Mark ~ 11 --~' . ~ :, : .. ~ . : : ~, . .:
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PATEN'r ~090-30~2 Example 6 A sur~ace of a sheet of tempered gla~;~; was thoroughly cleaned. To this surface was applied, ~y spraying/ the primer o~ Example ~ in an amount suf f icien~ ~o provide th~
organosilane and organoti'canate at a level of ~bou~ 3 gm per square meter and allowed to air dry.
S~bsequently, the coating composi~ion of example 4 above was applied by sprayir~g to a thicknes~ of about :L25 microns and allowed to air dry. The coa~ed glass was th~n baked at 245C for 15 min. An opaque uniform ~ilm is f ormed O
A portion of the glass is submerged in boiling water ~or 2 hours. Anoth~r portion of the glass is submerged in water for 7 days at 60C. In both case~;, there is no loss of coating, indicating excellent adhesion.

Example 7 Tempered glass was ~ aned, primed with ~he 2 0 composill:ion of Exa~ple 1 in an amount to provide the organosilane and organotitanate at a level of about 3 gm per square meter. Then the coa~ ing compositi.on of Example 4 wa~
applied a~ per Ex~mple ~. Subs~quently, ~he pigmented coating of Example 7 was applied by spr2~ying over ~he ~irst coating co~npo~ition to a thickn~;s o~ 125 microns~ Aftex dryillg/ th~ glass was again ~aked at 24SC fc~r 15 mi:n. When viewed through the glass the f irs~ oating appears uni~orm with high gloss and excellent del?~h o~ age and with no chang~ in appearance caused ~y ~e ses:ond coa~ing. From the opE30site side, th~ glass c:o ted with two coating compo~itions app~ars unifo~n with no show-~hrough of the first coating composition.

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2 ~ 7 PATENT

While the invention h~s been described in terms of certain preferred embodiments, modifications obvious to one with ordinary skill in t~e art may be ma~ea without depar~ing from the scope of the present invention.
Various features of the invention are set ~orth in the following claims.

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Claims (12)

1. A method of providing a pigmented coating to a glass substrate comprising priming said glass substrate by coating it with a clear coat which comprises a organosilane and organotitanate at a weight ratio of between about 5:1 and about 1:5 and coating said primed glass substrate with a coating composition comprising a fluorocarbon, an organosilane and/or an oryanotitanate, a thermoplastic acrylic resin having no functionality reactive with said organosilanes or said organotitanates, and inorganic pigment, said components being carried in an organic solvent and applied at between about 10 and about 55% solids.

2. A method in accordance with claim 1 wherein said fluorocarbon is polyvinylidene fluoride.

3. A method in accordance with claim 1 wherein said fluorocarbon comprises between about 50 and about 90 wt.
percent of said coating composition, said thermoplastic acrylic resin comprising between about 10 and about 50 wt. percent of said coating, said organosilane being at levels of between about 2 and about 12 phr and said pigment being at levels from about 2 to about 150 phr.

4. A method in accordance with Claim 1 wherein said primer is applied to provide organosilane and organotitanate to said glass substrate, in total, at between about 1.0 and about 5.0 gm. per m2.

5. A method in accordance with claim 1 wherein said applied coating composition is subsequently baked at between about 200 and about 250°C.

6. A method in accordance with Claim 1 wherein said clear coat contains organosilane and organotitanate at a weight ratio of between about 2:1 and about 102.

7. A product of the process of Claim 1.

8. A method of coating a single surface of a glass substrate to provide two distinct appearances when viewed from opposite sides, the method comprising priming said glass substrate by coating it with a clear coat which comprises a mixture of an organosilane and an organotitanate at a weight ratio of between about 5:1 and about 1:5 and, coating said primed glass substrate with a coating composition comprising a fluorocarbon resin, an organosilane and/or an organotitanate, a thermoplastic acrylic resin having no functionality reactive with said organosilanes or said organotitanate, and inorganic pigment, said components being carried in an organic solvent and applied at between about 10 and 55% solids, and applying a second coating composition to said first coating comprising polyvinylidene fluoride, an organosilans, an acrylic binder having no functionality reactive with said organosilanes, and inorganic pigment, said first and second coatings being pigmented or colored to provide distinctly different appearances, each of said first and second coatings being applied to a thickness to make each completely opaque.

9. A method in accordance with claim 8 wherein said fluorocarbon in each of said coating compositions comprises between about 50 and about 90 wt. percent of said coating composition, said thermoplastic acrylic resin comprising between about 10 and about 50 wt. percent of said coating, said organosilane being at levels of between about 2 and about 12 phr and said pigment being at levels from about 10 to about 150 phr.

10. A method in accordance with Claim 8 wherein said primer is applied to provide organosilane and organotitanate to said glass substrate, in total, at between about 1 and about 5 gm. per m2.

11. A method in accordance with claim 8 wherein said applied coating compositions are subsequently baked at between about 200 and about 250°C.

12. A product of the process of Claim 8.